Lead components have long been used to impart many desirable properties in glaze and enamel compositions for dinnerware. Unfortunately, improperly formulated or improperly fired lead glazes or enamels allow hazardous levels of Pb to be released from the ware's surface. The Food and Drug Administration (FDA) has established action levels for maximum Pb release from earthenware (Table 1). Ware determined to have a lead content at or above these levels will be subject to possible regulatory action by the FDA. The FDA monitors both domestically produced and imported dinnerware on a routine basis. The AOAC (Association of Official Analytical Chemists) or equivalent ASTM (Annual Book of ASTM Standards (1987) 5.02, 314-316) test methods for Pb are used in the United States. Both of these methods require extraction (leaching) of 6 pieces of ware for 24 hours with 4% acetic acid at room temperature. This leach solution is analyzed for Pb by flame atomic absorption spectroscopy.
TABLE 1 ______________________________________ Current FDA Action Levels for Maximum Pb Released from Earthenware Action Level Category Action Basis (ug Pb/ml) ______________________________________ Flatware Average of 6 units 7 Small hollowware (&lt;1.1 L) Any one of 6 units 5 Large hollowware (&gt;1.1 L) Any one of 6 units 2.5 ______________________________________
A representative test technology is exemplified by U.S. Pat. No. 3,809,537, of which Example 17 is typical. The ware being tested is leached by a solution of acetic acid in water (or as in the patent, white vinegar) for various periods of time ranging from 30 minutes to 24 hours. The process of this patent requires a 24 hour leach period which saves no time relative to the Official Methods of Analysis, sec. 25.024-0.027, 14th ed. (1984) pub. by AOAC) and is qualitative at best. Other methods claim results after only 30 minutes of contact. (See Official Methods of Analysis, sec. 25.028-25.030).
The short-term leach methods require extensive chemical operations, such as the adjustment of hydrogen ion concentration, the extraction by an immiscible solvent containing the complex, and an estimation of the depth of color produced. Some of these methods are viewed as being quantitative. These extensive operations are required because the large volumes of acetic acid solutions required to fill the test vessel dilute the lead released and for that reason, a very sensitive and complex method is required.